I think that'd have made the game sound really, well, bad. Because if you want to name them something that isn't in their database, then it all goes wrong. For example, if I wanted to name Tidus a Welsh name like Erfyl (as an example- it's actually my Uncle's name) then it wouldn't be pronounced correctly...I think they should use some kind of algorism or voice program,I don't know,that let the characters call you by the name you wrote in the blank space. Do remember seeing something like that on some voice programs.
Or,well,just call him the name it's supposed to be and that's just fine,lol.